While methodologies of collecting optical information about a target tissue (such as a biological tissue) with various probes are many, most of those make use of some optical channel, operably connecting the target and the optical detector unit (such as a CCD camera with an accompanying electronic circuitry), and a mechanism of dispersing the light collected from the target into components that, when analyzed independently from one another, often provide complementary information about the target. The optical channel is sometimes structured as a “fiberscope” (in which case light is channeled between the proximal and distal ends of the flexible probe by at least one dedicated optical waveguide) and, alternatively, the optical channel may employ a system of lenses (disposed in and supported by a rigid tubular body) that act as an optical relay of the now-rigid endoscope.
A typical non-limiting example of the family of such endoscopes is provided by laparoscopes, which are often used to provide access to the target tissue through small incisions made in a body. Since the user does not have direct access or vision of the site of interest, the quality of the image provided by the endoscope is of paramount importance. Other operational parameters cannot be discarded either—one of those being the size and weight of the endoscope.
It is recognized that the laparoscopes employing a lens-based relay system, often referred to as proximal sensing laparoscopes, can be relatively large, because the optical sensors of such devices are disposed in operation outside of the body. As a corollary of the use of optical lenses, however, these devices afford good photonic, optical, and electrical performance and remain dominant in practice. The fiberscope-based laparoscopes also have their optical detection units affixed to ends of the fiberscopes. An alternative option of constructing a laparoscope, in which a small CCD or CMOS sensor is disposed inside the laparoscope immediately at the objective of the laparoscope, attracted attention with advances in imaging sensor technology and miniaturization. These are referred to as distal sensing laparoscopes and, due to the chosen configuration, these devices are devoid of complexities of fiber bundles and/or relay optics that related technologies are used to rely on.
Endoscopic (and, in particular, laparoscopic) systems of related art have many shortcomings. For example, proximal sensing laparoscopes must use relay optics to transmit the image through the laparoscope. The misalignment of each optical element vignettes the final view, resulting in poor performance. Improvements in alignment schemes have been produced, yet most are bought through experience and proprietary methodology. Images formed with the use of a fiberscope are pixilated, in direct relation to the thickness and position of each fiber with respect to the optical detector, resulting in a grating effect on the image and a significant reduction in resolution. While distal sensing laparoscopes may avoid these problems, their operation is disadvantageously affected by the small diameter of the laparoscope. Often, laparoscopes measure 5 mm to 10 mm in diameter, so the optical sensors must be even smaller to fit in the limited space provided by the interior of the laparoscope.
The laparoscope devices are sometimes structured to provide two optical channels—in practice, by combining two small diameter laparoscopes bundled together, side by side, in a regularly-sized package. The image from one optical channel is delivered to the left eye of the user, while the image corresponding to another optical channel is delivered to the right eye of the user. Utilizing video cameras and modern means of displaying three-dimensional (3D) images (such as switching LCD glasses, polarized glasses, head mounted displays), the operator is often able to perceive the 3D image from the perspective of the two-channel laparoscope. Such “3D laparoscopes” are extremely demanding on optics and electronics packaging dimensions. This significantly reduces the design space.
If required, the laparoscopic systems may be operationally enhanced by extending the range of wavelengths of light sensed at the image sensor to those beyond visible light. The most useful of these wavelengths are those in the NIR and IR portions of the spectrum, as absorption of these wavelengths by biological tissue is relatively low. While light at wavelengths up to 2 microns, has been shown to aid in the identification of cancers and different biological tissues, the operational range of currently-existing laparoscopic systems does not extend beyond the NIR wavelengths. For example, NIR fluorescent dyes such as indocyanine green (ICG) may be introduced into the bloodstream or otherwise affixed to the tissue used to identify blood vessels during surgery. Profusion of blood in some cases can be used to identify tumors in organs. These types of image sensors are incorporated into state of the art laparoscopes, but only in proximal sensing laparoscopes.
When an endoscope is intended to operate at multiple wavelengths, it can be equipped with a three-sensor optical camera which is configured to include three CCD/CMOS sensors, for example, and the objective lens which is disposed such that a series of dichroic or bandpass prisms split the incoming from the target light into individual components (for example, those in red, green, and blue portions of the spectrum) before reaching the sensors. Each component of incoming light signal is then detected by a single sensor. (This is opposed to a single-sensor camera that utilizes color filters over the detector to provide for the RGB channels for a color image.) To maintain equal focal lengths in each of the sought-after spectral regions, compact footprint, modern three-sensor cameras utilize a Philips-style dichroic prism 100, shown in FIG. 1. The advantage of the Philips-style three sensor camera is that a user is no longer limited by the ability to create micron-by-micron square, color filters on the sensor. This frees up the design space of the sensor. Additionally, there is no longer any demozaicing needed with the traditional Bayer filter (resulting in higher true-color resolution). While these advantages are recognized, the Philips-style dichroic prism is known to be too large to fit within the size constraints of a distal sensing laparoscope (containing either one or two optical channels). In fact, the Philips-style prism is substantially larger than any of the image sensors used with it. Accordingly, the space of operation of such arrangement is limited to the proximal sensing probes, which are not under constraints of limited space of the housing hosting an optical channel of the laparoscope. Other beam-splitting optical systems that could be used to separate light delivered by an optical channel of an endoscope towards the optical detection unit often at least partially block delivered light, thereby deteriorating the resulting images by at least reducing the range of spatial frequencies of the incoming light.
Accordingly, there remains a need for improvement of laparoscopic imaging technology that overcomes the aforementioned shortcomings.